1. Field of the Invention
The present invention relates to a read head with improved lead layers at an air bearing surface and more particularly to high resistance lead layer portions of first and second lead layers that have improved dimensions and performance.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS to cause the slider to ride on an air bearing a slight distance from the surface of the rotating disk. The write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A magnetic gap is formed between the first and second pole piece layers by a write gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field across the gap between the pole pieces. This field fringes across the gap at the ABS for the purpose of writing information in tracks on moving media, such as in circular tracks on a rotating disk.
The read head includes first and second shield layers, first and second gap layers, a read sensor and first and second lead layers that are connected to the read sensor. The first and second gap layers are located between the first and second shield layers and the read sensor and the first and second lead layers are located between the first and second gap layers. The distance between the first and second shield layers determines the linear read density of the read head. Accordingly, the first and second gap layers are constructed as thin as possible without shorting the lead layers to the first and second lead layers. High linear density results in more bits being read by the read head per length of magnetic track passing by the read head on the rotating disk.
Each of the first and second leads has a high resistance lead layer and a low resistance lead layer. Each high resistance lead layer is a material that is resistant to corrosion since it has an edge exposed at the air bearing surface. The high resistance lead layer typically includes a film made of tantalum (Ta). Each low resistance lead layer is corrosive, but this is of no consequence since it is protected from the outside environment by being recessed in the head. The low resistance lead layer typically includes a film made of copper (Cu) or gold (Au).
The high resistance layer has multiple films. One of the films is the Ta film for conducting a sense current through the read sensor. Another one of the films is a hard bias film for longitudinally biasing the read sensor so that it is magnetically stabilized to prevent Barkhousen noise. In the past each high resistance lead layer extended from a respective side edge of the read sensor in a lateral direction (parallel to the ABS) before it extended back into the head to make contact with the low resistance lead layer. The longer the extension of the high resistance lead layer the thicker the high resistance lead layer has to be in order to maintain its resistance at an acceptable level. When the resistance gets too high the read head is damaged by heat. When the extension of the high resistance lead layer is made thicker in order to keep its resistance down planarization between the top surfaces of the read sensor layer and the high resistance lead layers is degraded.
The read sensor is bounded by a front edge at the ABS, first and second side edges that extend perpendicular to the ABS and a back edge that is spaced from the ABS and that defines a stripe height of the read head. Each high resistance lead layer has a forward edge that makes contact with a respective one of the first and second edges of the read sensor. This type of connection is referred to in the art as a contiguous junction. When the high resistance lead layers are thickened in order to reduce resistance their top surfaces are elevated with respect to the top surface of the read sensor. This causes a step adjacent each side edge of the read sensor. Unfortunately, these steps are replicated through the second gap layer and the second shield/first pole piece layer all the way to the write gap layer of the write head. Since the write head has to be made wider than the read head the write gap replicates these steps and takes on a curvature that seriously affects the write capability of the write head. The curved write gap causes the write head to write curved bits (magnetic signals) on the rotating track. When the straight across read head reads these curved bits it progressively loses magnetic intensity from a center of the bit toward outer edges of the track. Accordingly, there is a strong felt need to promote planarization of the read sensor and the high resistance leads so as to reduce write gap curvature.
We sought a method to construct the lead layers that would promote planarization between the read sensor and the high resistance lead layers at the ABS. One method investigated constructs the high resistance lead layers before the low resistance lead layers. In this method a read sensor material layer is deposited over an entire wafer. A first mask is formed that has openings at the high resistance lead layer sites which extend to the first and second side edges of the read sensor. Read sensor material is milled out at the high resistance lead layer sites and the high resistance lead layer material is deposited to form first and second high resistance lead layers at the high resistance lead layer sites that make contiguous junctions with the first and second side edges of the read sensor. This establishes the track width of the read. Track width density (number of tracks per inch of the magnetic disk) times the aforementioned linear density is the areal density of the read head. Increasing the areal density increases the bit density (number of bits per square inch of the magnetic medium) of the disk drive. The first mask is removed and a second mask is formed that covers the read sensor and the high resistance lead layers. All exposed read sensor material is then milled away to define the back edge and stripe height of the read sensor. The stripe height is important in establishing the magnetics of the read sensor. The second mask is then removed and a third mask is formed that has openings at low resistance lead layer sites. Low resistance lead layer material is then deposited that forms first and second low resistance lead layers that overlap and engage the first and second high resistance lead layers. The third mask is then removed.
Unfortunately, the aforementioned method of making subjects the high resistance lead layers to subsequent processing since they are constructed before defining the se height of the read sensor and before constructing the low resistance lead layers. Since the second mask must be slightly inboard of the outer edges of the high resistance layer in order to ensure complete removal of unwanted read sensor material an outer edge portion of each high resistance lead layer is subjected to milling. Reduction of the high resistance layers due to subsequent processing requires that the thickness of the high resistance layers be increased as deposited in order to satisfy the resistance requirements. As stated hereinabove, thicker high resistance leads results in increased write gap curvature. Accordingly, there is a strong felt need to provide a method of making the read sensor leads that will not contribute to thicker high resistance lead layers.
Instead of extending the high resistance lead layers laterally before making a turn to connect to the low resistance lead layers the present invention extends the high resistance lead layers straight back into the head from each of the first and second side edges of the read sensor. This lessens the length of the each of the high resistance lead layers so that they do not have to be made thicker to satisfy the resistance requirements. Accordingly, a lateral width of each high resistance lead portion along the ABS and a thickness thereof are chosen so as to minimize the thickness while satisfying the resistance requirements.
Further, a method of making the first and second lead layers is provided that minimizes the thickness of the high resistance lead layers. Instead of constructing the high resistance lead layers first, the present method constructs the high resistance lead layers last. After depositing read sensor material over a wafer a first mask is formed that has openings at the low resistance lead layer sites. After milling the read sensor material from the low resistance lead layer sites low resistance lead layer material is deposited. This forms the first and second low resistance lead layers. A second mask is then formed that covers the read sensor site and the low resistance lead layers. The second mask has a large opening that exposes all unwanted read sensor material and has an edge that is located at the desired back edge (stripe height) of the read sensor. The read sensor material is milled away and the second mask is removed leaving the read sensor with a desired stripe height. Next the third mask is formed with openings at the first and second high resistance lead layer sites. After removing read sensor material at the first and second high resistance lead layer site high resistance lead layer material is deposited to form the first and second high resistance lead layers. The third mask is then removed. The high resistance lead layers are now complete and are more predictable since they have not been subjected to processing steps in the construction of the low resistance lead layers and the read sensor.
The present invention provides a special step after forming the second mask and milling away the unwanted read sensor material. The second mask covers the read sensor site as well as a portion of read sensor material layer adjacent first and second edge sites of the read sensor site. The second mask cannot define the first and second edges of the read sensor since this is the function of the third mask which implements a contiguous junction between the high resistance lead layers and the side edges of the read sensor. Accordingly, the second mask leaves some unwanted read sensor material adjacent each edge of the read sensor site. When the third mask is formed the openings therein expose this unwanted read sensor material as well as a portion of the first gap layer where unwanted read sensor material was removed during the second masking step. It should be noted that if each opening in the third mask did not expose some of the first gap layer there would be no assurance that all read sensor material was removed except at the read sensor site. Without protection the first gap layer is exposed to a developer for patterning the third mask and an ion milling process after patterning the third mask. The developer and the ion milling will seriously damage the insulating quality of the first gap layer. This problem has been overcome in the present invention by depositing an insulation refill material after milling has occurred in the second masking step. The insulation refill material will now be adjacent the unwanted read sensor material in each opening of the third mask. Accordingly, when milling is implemented the milling mills insulation refill material as well as the read sensor material. In the preferred embodiment the thickness of the refill insulation material is designed so that the refill insulation material and the read sensor material are consumed at the same time in each of the openings of the third mask at the high resistance lead layer sites. This then exposes the first gap layer with no damage. The high resistance. lead layer material can then be deposited in the openings in the third mask. The third mask is then removed.
An object of the present invention is to provide a read head with improved high resistance lead layers at the ABS.
Another object is to provide a minimal extension of the high resistance lead layers of a read head so that their thickness does not have to be increased to satisfy resistance requirements.
A further object is to provide a read head with first and second lead layers that are more planarized with respect to a read sensor.
Still another object is to provide a read head that does not adversely impact the straightness of a write gap layer of a write head.
Still another object is to provide a method of making first and second lead layers of a read head that promotes planarization of the lead layers and a read sensor.
Still other objects and advantages of the invention will become apparent upon reading the following description taken together with the accompanying drawings.